Schistosoma japonicum and colorectal cancer: an epidemiological study in the People's Republic of China.

Prevalence of infestation with Schistosoma japonicum was highly correlated with mortality from colorectal cancer in 89 communes in four counties of Jiangsu province, China (rank correlation coefficient = 0.68) in 1973-75, and with incidence of colorectal cancer in 24 communes of Haining county, Zhejiang province in 1977-79. No similar correlations were seen with lung cancer. The presence or absence of a past history of schistosomiasis was ascertained from 154 patients with cancer of the rectum, 98 patients with cancer of the colon and two sets of individually matched control patients. One set consisted of patients with non-gastrointestinal cancer and the other of near neighbours of the colorectal cancer patients. In patients with a history of schistosomiasis, relative risk of rectal cancer was 8.3 (95% confidence interval 3.1 to 22.6) when other cancer patients were used as controls and 4.5 (95% confidence interval 1.7 to 12.1) with neighbourhood controls. Relative risk of colon cancer was not significantly increased (1.20 with 95% confidence interval 0.48 to 3.18 in a matched triplet analysis) in association with schistosomiasis.